"Did you just come up with the saddest things you can think of and put them on pieces of paper and then put them in the most depressing hat imaginable?" That's how "Colbert Report" host Stephen Colbert asked author John Green about the inspiration behind beloved cancer drama "The Fault in Our Stars" last night.

While Green's novel formed the foundation for the box office success starring Shailene Woodley, the writer is more than an author of young adult fiction, which Colbert brought up -- thanks to his "Vlogbrothers" work on YouTube with brother Hank Green, the author is incredibly popular online, especially among young fans.

"Are you a cult leader?" Colbert asks -- a question Green flips right back around on him. Both men, it's clear, have their followings.